The present invention relates to precision measuring machines, and in particular to a real-time data collection apparatus for collecting data from an automated multi-axis measuring machine.
Precision measuring machines, such as the universal measuring machine manufactured by Moore Special Tool Co., Inc., the assignee of the present invention, are used to verify many types of physical dimensions on work pieces, including precision mechanical parts used in the aerospace industry and the like. Such machines are also used by standards bureaus and metrology laboratories to verify accuracies in increments as small as millionths of an inch.
In recent years, a rapid proliferation of computer-based coordinate measuring machines have been introduced into the marketplace. Such systems have been made possible by the advent of low-cost microprocessors. In most such systems, a microprocessor-based data-processing circuit is placed between the measuring elements of the machine and the digital display which outputs measurement data to the machine operator. The result has provided coordinate measuring machines with low-cost digital readouts and built-in data-collection and analysis functions. A good background of such coordinate measuring machines ("CMMs") is provided in an article entitled "Taking The Measure Of CMMs", George Schaffer, American Machinist, Special Report 749, October 1982, pages 145-160.
In some measuring applications, particularly those where extremely high accuracy is required, it is desirable to use an analog probe in the measuring machine to provide an accurate, limited-range, linear output signal proportional to its deflection. In using such an apparatus, the probe is moved with respect to the workpiece until contact is made. The machine coordinate and probe-head readings are added to provide the measuring result, with the probe data representing actual deviation from the measured coordinate data. However, in order to produce a precise result, it is imperative that the measured coordinate data and probe data be obtained simultaneously. Past coordinate measuring machines do not achieve the precise real-time simultaneous collection of data which is necessary to provide the high accuracies desired by some users of such machines. The present invention provides such accuracies by capturing or "latching" data from all of the measuring machine axes and a probe simultaneously.
Techniques have been used in the past to latch data from digital probes upon contact of the probe with a work surface. For example, such a technique is disclosed in a paper entitled "Electrical Touch Probe For XYZ Coordinate Measuring Machine", John W. Ayres and Harold S. James, Proceedings Of Southeastcon '80, Nashville, Tenn. (.COPYRGT. IEEE, April 1980). The data from the digital probes disclosed is directly indicative of the machine coordinates. Thus, the problem of simultaneously reading data from an analog probe together with separate machine coordinate data is not present. Another technique for latching probe data is disclosed in U.S. Pat. No. 3,551,649 entitled "Position Measuring System". Again, there is no disclosure of the simultaneous reading of data from separate machine coordinate sensors and an analog probe. Instead, data are clocked, from each of a plurality of probes into a register for the probe data, independently for each probe. Similarly, U.S. Pat. No. 3,481,042 entitled "Surface Sensing Apparatus" discloses apparatus wherein probe data is gated only upon contact of the probe with the workpiece.
In U.S. Pat. No. 4,181,958 a scheme is disclosed for a "Multiple Probe Gauge System" wherein the analog output signal of a plurality of probes is successively sampled, digitized and stored. The stored information is then digitally processed by a microprocessor to produce a digital signal which is a function of the analog output signals of selected probes. Like the other references discussed hereinabove, this patent also fails to disclose a system wherein coordinate measurement data and probe data are simultaneously captured or latched to provide for highly accurate measurements.
Accurate measuring systems have been constructed in the past using laser interferometer techniques to provide measurements along multiple axes. An example of such an apparatus is shown in U.S. Pat. No. 3,661,463 entitled "Single Interferometer Multiple Axis Laser Measuring System". In the measuring machine shown in that patent, however, there is no probe for measurement of minute deviations from the coordinate measurements provided by the laser system.
It would be advantageous to provide an automated multi-axis measuring machine having accuracies on the order of millionths of an inch. Such a machine should utilize an analog probe in combination with sensors (e.g. laser interferometers) providing measurement data along each of the machine's axes, to provide deviation readings along the axes. In order to ensure the accuracy of measurements, data from the probe and data from the sensors should be captured concurrently for reading by appropriate data processing components. Such an apparatus would, in effect, take periodic "snapshots" of data from the probe and sensors to provide real-time data collection of desired measurements.
The present invention relates to such a measuring apparatus.